The present invention relates to a magnetoresistive reproducing head used for playback of magnetic disk apparatuses or magnetic tape apparatuses such as VTRs.
Recent magnetic recording apparatuses have increased recording capacity. To accomplish this, as an example, the magnetic disk apparatus is made to have a track width as narrow as 5-6 .mu.m. As the size of the apparatus decreases, the media velocity also decreases. In order to detect signals recorded in such narrow areas at a high signal-to-noise ratio, magnetoresistive heads have been developed in place of the conventional inductive heads. As an example, the magnetoresistive head is made in a structure shown in FIGS. 3(a) and 3(b) (see, for example, the Japanese Patent Laid-Open 60-45922 and the Digests of 13th Annual Conference on Magnetics in Japan, 1989, pp. 228). The magnetic head shown in these figures are called a shunt bias magnetoresistive head. FIG. 3(a) is a plan view for the head, and FIG. 3(b) is a cross-sectional view taken across line A--A' in FIG. 3(a).
The magnetoresistive head comprises a lower shield film 2, a lower gap film 3, a magnetoresistive film 4, a shunt bias film 5, an electrode 6, an upper gap film 7, and an upper shield film 8 laminated on a non-magnetic substrate 1. In general, all the films except the lower shield film 2 and the upper shield film 8 are made very thin. The magnetoresistive film 4, for example, is a few 10 nm thick, and the lower gap film 3 and the upper gap film 7 are around 0.2 .mu.m.
In order to allow the magnetoresistive head to play back the high density recorded signals with a high signal-to-noise ratio, the magnetoresistive film 4, the upper gap film 7 and the lower gap film 3 are formed very thin. With such thin films, the under film of the film to be etched is undesirably subjected to etching during patterning. In the worst case, the under film may vanish, particularly when the film to be etched is thick relative to the thin under film. In the magnetic head shown in FIGS. 3(a) and 3(b), the problem of undesirable etching of the upper gap film 7 and the electrode 6 formed under the upper gap film 7 occurs in patterning the upper shield film 8.
In general, the thin film formed under the film to be etched for patterning is adversely subjected to etching because of the film thickness distribution and the etching rate distribution within and between the substrates. In particular, the undesirable etching is significant in physical etching methods, such as an ion milling, which have been frequently used in fabricating magnetic heads. As for the magnetoresistive head, as described above, it is formed of very thin films, and the unwanted etching of the under films tends to lower the yield to a great extent.